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Develop Guidelines for the Design and Construction of Ultra-Thin Asphalt Concrete Overlays


Ultra-thin asphalt concrete (AC) overlays are defined as having a thickness of 1 inch or less which are to be used as the final wearing surface. In addition to the economic benefit of ultra-thin overlays there are many instances where the use of very thin overlays is desirable. Often geometric concerns, bridge clearances, curb and gutter situations mandate that only thin overlays are possible. A research study is required to provide a concise guide to designing and constructing these overlays.


A study is required to provide guidelines on the design and construction of ultra-thin AC overlays. It is critical to summarize the existing design methodologies, material quality requirements, construction and performance information. It is necessary to develop concise evaluation, design and construction guidelines for DOT's wishing to evaluate the use of these materials. These recommendations must include minimum aggregate quality requirements. It is intended that these mixes should also be designed by DOT's using available equipment (SUPERPAVEā„¢) with possible additional performance tests. The performance tests will as a minimum evaluate both rut and reflection cracking resistance. It is also critical to include the condition of the existing pavement in establishing the desirable engineering properties of the ultra-thin overlay.


With the escalating cost of asphalt materials it is critical that cost effective solutions be developed for the maintenance of existing highway networks. It is anticipated that the ultra-thin mixes will be 20 to 30% more expensive than traditional materials, but if the can be placed in 1 inch, as opposed to traditional 2 inch lift, the economic payoff's are clear.

These mixes are already being used in several DOT around the US. However the performance of these mixes has not been documented. The lessons learned need also to be documented. There is an urgent need to accelerate nationwide implementation of ultra-thin overlays.

Related Research:

Several DOT's have developed specifications for very thin overlays. The Ohio DOT has used its "smoothseal" mix since the mid-1990's. These mixes are reported to be rut resistant and maintain excellent skid properties. Other DOT's such as Arizona, Maryland and Michigan also have specifications for ultra-thin overlays. The National Center for Asphalt Technology has been researching "screenings mixes" which have been shown to have excellent rut resistance. The Texas DOT has developed and field tested a Crack Attenuating Mix which is being specifically designed to pass both a rutting and cracking requirements, initial performance results have been promising. Other DOT's have also been active in this area but no systematic evaluation has been made of overlay performance.


This project will be divided into 2 phases. In Phase 1 the researchers will:

a) Summarize existing DOT practices and performance. This will include visits to at least 4 States which have placed Ultra-thin overlays. As a minimum the performance will as a minimum include rutting, reflection cracking and skid performance.

b) Use the information collected to develop guidelines on:

  1. How to select candidate projects (including structural evaluation and recommendations on when ultra thin overlays are not recommended)

  2. How to design these mixes based on existing pavement condition, pavement type and environment

  3. Construction recommendations (QC/QA recommendations)

In Phase 2 the research agency will be required to work with 3 DOT's. Each state DOT nominates two pavements for consideration as candidates to receive an ultra-thin overlay. The researchers will conduct a structural evaluation of both and then to design ultra thin HMA mixes based on their locally available aggregates. The results from the evaluation and mix design will be presented to DOT engineers.

All the findings from Phases 1 and 2 will be included in the studies final report.

Sponsoring Committee:AKP30, Design and Rehabilitation of Asphalt Pavements
Research Period:24 - 36 months
Research Priority:Medium
RNS Developer:Trenton Clark
Date Posted:01/27/2014
Date Modified:01/28/2014
Index Terms:Asphalt concrete pavements, Overlays (Pavements), Pavement design, Guidelines, Ultra-thin, Thickness, Economic benefits,
Cosponsoring Committees: 

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